• 콘크리트학회논문집
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• 제16권6호
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• pp.867-873
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• 2004

It has been known that debonding failures between CFS(Carbon Fiber Sheet) and concrete in the strengthened RC beams are initiated by the peeling of the sheets in the region of combined large moment and shear forces, being accompanied by the large shear deformation after flexural cracks. These shear deformation effects are seldom occurred in small-scale model tests, but debondings due to the large shear deformation effects are often observed in a full-scale model tests. The premature debonding failure of CFS, therefore, must be avoided to confirm the design strength of full-scale RC beam in strengthening designs. The reinforcing details, so- called 'U-Shape fiber wrap at mid-span' which wrapped the RC flexural members around the webs and tension face at critical section with CFS additionally, were proposed in this study to prevent the debonding of CFS. Other reinforcing detail, so called 'U-Shape fiber wrap at beam end' were included in this tests and comparisons were made between them.

• 콘크리트학회지
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• 제11권1호
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• pp.201-208
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• 1999

철근콘크리트 구조물은 과도한 하중과 유지관리의 소홀 등 여러 가지 이유로 보수${\cdot}$보강을 필요로 하는 경우가 많다. 이에 대해 국내에서는 철근콘크리트구조체의 보강방법으로 강판, 탄소섬유쉬트, 탄소섬유판을 사용하고 있다. 그러나 이들 보강재료의 성능에 대하여 신뢰할 만한 연구 결과가 아직까지 충분치 않은 실정이다. 본 연구는 보강재의 종류, 균열폭, 하중의 재하상태를 변수로 보강된 철근콘크리트보의 거동을 규명하고자 하였다. 보수시험체의 경우 기준시험체와 내력과 연성은 비슷한 거동을 나타냈으나 파괴형상은 인장부위 콘크리트의 탈락과 지압파괴가 발생하였다. 보강시험체의 경우, 보강의 효과는 뚜렷이 나타났으나 보강재의 물성을 100% 발휘하지는 못하였다. 탄소섬유쉬트의 경우 접착제의 성능이 완벽하지 않아 최대 내격시의 변형률이 파단시의 변형률과 비교하여 66%정도로 나타났다. 또한 보강시의 균열폭과 하중의 유${\cdot}$무는 부재의 내력과 거동에 영향을 거의 미치지 않는 것으로 나타났다.

• Structural Engineering and Mechanics
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• 제30권2호
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• pp.247-261
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• 2008

Performance of shear-deficient reinforced concrete (RC) beams strengthened with carbon fiber-reinforced polymer (CFRP) strips/sheets is analyzed through numerical simulations on four-point bending tests. The numerical simulations are carried out using the finite element (FE) program ABAQUS. A micromechanics-based constitutive model (Liang et al. 2006) is implemented into the FE program ABAQUS to model CFRP strips/sheets. The predicted results are compared with experiment data (Khalifa and Nanni 2002) to assess the accuracy of the proposed FE analysis approach. A series of numerical tests are conducted to investigate the influence of stirrup lay-ups on the shear strengthening performance of the CFRP strips/sheets, to illustrate the influence of the damage parameters on the microcrack density evolution in concrete, and to investigate the shear and flexural strengthening performance of CFRP strips/ sheets. It has been shown that the proposed FE analysis approach is suitable for the performance prediction of RC beams strengthened with CFRP strips/sheets.

• Composites Research
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• 제13권3호
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• pp.1-8
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• 2000

Excellent environmental durability and handy installation procedure as well as high specific strength and stiffness have introduced fiber-reinforced polymeric composite materials into the civil and architectural engineering field. This study presents the considerably enhanced strength characteristics of the mortal beams by being reinforced with epoxy-bonded carbon fiber sheets(CFS). Three point bending and Charpy impact tests were performed on both of bare and reinforced mortar specimens. The influences of length, and the number of reinforcing plies were investigated. Strength reduction due to pre-existent notch was lessened dramatically. The acoustic emission(AE) measurement revealed the progressive damage process in reinforced specimens.

• Steel and Composite Structures
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• 제19권2호
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• pp.441-465
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• 2015

This paper presents the experimental results of flexural and compression steel members strengthened with carbon fiber reinforced polymers (CFRP) sheets. In the flexural test, the five specimens were fabricated and the test parameters were the number of CFRP ply and the ratio of partial-length bonded CFRP sheets of specimen. The CFRP sheet strengthened steel beam had failure mode: CFRP sheet rupture at the mid span of steel beams. A maximum increase of 11.3% was achieved depending on the number of CFRP sheet ply and the length of CFRP sheet. In the compression test, the nine specimens were fabricated and the main parameters were: width-thickness ratio (b/t), the number of CFRP ply, and the length of the specimen. From the tests, for short columns it was observed that two sides would typically buckle outward and the other two sides would buckle inward. Also, for long columns, overall buckling was observed. A maximum increase of 57% was achieved in axial-load capacity when 3 layers of CFRP were used to wrap HSS columns of b/t = 60 transversely.

• Steel and Composite Structures
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• 제23권4호
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• pp.385-397
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• 2017

Currently, CFRP (Carbon Fiber Reinforced Polymer) plate bonding is used quite extensively as a strengthening method. In this technique, a composite CFRP plate or sheet of relatively small thickness is bonded with an adhesion material to steel or concrete structure in order to improve its structural behavior and strength. The sheets or plates do not require much space and give a composite action between the adherents. In this study, the rotation capacity of CFRP-strengthened cold-formed steel (CFS) beams has been evaluated through numerical investigation. Studies on different structural levels have been performed. At the beam level, C-section has been adopted with different values of profile thickness, web height, and flange width. At the connection level, a web bolted moment resistant type of connection using through plate has been adopted. In web-bolted connections without CFRP strengthening, premature web buckling results in early loss of strength. Hence, CFRP sheets and plates with different mechanical properties and geometric configurations have been examined to delay web and flange buckling and to produce relatively high moment strength and rotation capacity. The numerical results reveal that CFRP strengthening may increase strength, initial stiffness, and rotation capacity when compared with the case without strengthening.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1997년도 봄 학술발표회 논문집
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• pp.598-604
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• 1997

In recent years, strengthening by epoxy-bonded steel plates, carbon fiber sheets, aramid fiber sheets and so on, is spotlighted. Among them, the method using steel plates is most widely applied. Most studies have dealt with strengthening by epoxy-bonded steel plates. However the actual behavior of strengthened RC beams are not well established. Particularly, the studies on the separation load thar affects failure load of the beam are relatively insufficient. In this study, test parameters are the magnitude of pre-load, plate length, plate thickness, existence and spacing of anchor bolt, the number of plate layer and the height of side strengthening, 17reinforced concrete beams are strengthened by steel plates according to test parameters. Deflection, failure load, strains of reinforcing bar, concrete and plate are measured from tests(4 points loading). The failure mode, and separation load are analyzed from these measured data. The difference between Robert's theory and test results is discussed, and the prediction equation for separation load in the case of rip off is proposed.

• Structural Engineering and Mechanics
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• 제72권3호
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• pp.305-312
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• 2019

This paper investigates the effect of utilizing vacuum bagging process to enhance the bond behavior between fiber reinforced polymer (FRP) composites and concrete substrate. Sixty specimens were prepared and tested using double-shear bond test. The effect of various parameters such as vacuum, fiber type, and FRP sheet length and width on the bond strength were investigated. The experimental results revealed that utilizing vacuum leads to improve the bond behavior between FRP composites and concrete. Both the ultimate bond forces and the maximum displacements were enhanced when applying the vacuum which leads to reduction in the amount of FRP materials needed to achieve the required bond strength compared with the un-vacuumed specimens. The efficiency of the enhancement in bond behavior due to vacuum highly depends on the fiber type; using carbon fiber showed higher enhancement in the bond strength compared to the glass fiber when vacuum was applied. On the contrary, specimens with glass fiber showed higher enhancement in the maximum slippage compared to specimens with carbon fibers. Utilizing vacuum does not affect the debonding failure modes but lead to increase in the amount of attached concrete on the surface of the debonded FRP sheet.

• 대한토목학회논문집
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• 제43권5호
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• pp.567-576
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• 2023

일반적으로 RC 보 부재는 휨 부재로서 휨 하중에 대해서만 고려하여 설계된다. 하지만, 실제 건축물에서는 부재 간의 연속성으로 인해 축력과 휨 하중을 동시에 받게 된다. 이로 인해 RC 보 부재의 휨 강도는 증가하지만, 변위는 감소하며, 균열은 주로 보의 중앙부에 집중되게 된다. 따라서 본 연구에서는 축력과 휨 하중을 동시에 받는 RC 보 부재에 탄소섬유시트를 이용한 보강에 따른 휨 성능을 실험적으로 평가하였다. 탄소섬유시트는 부재의 중앙부에 감싸 보강을 하였으며, 축력과 휨 하중을 부재에 가력하였다. 축력의 크기와 탄소섬유시트 보강에 따른 철근콘크리트 부재의 파괴 형태, 휨 강도, 처짐 및 연성을 분석하였다. 그 결과, 축력의 증가에 따라 최대 휨 강도의 상승이 발생하였지만, 연성은 최대 64%까지 감소하였다. 탄소섬유시트 보강을 통해 휨 강도는 최대 27% 증가하였으며, 휨에 의한 보의 최대 처짐은 8% 감소하였으며 연성은 최대 43% 증가하였다.

• Computers and Concrete
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• 제19권4호
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• pp.339-346
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• 2017

The main objective of this paper was to illuminate the effect of marine environmental condition on durability of reinforced concrete (RC)-corroded columns strengthened with carbon fiber reinforced polymer (CFRP) and glass fiber reinforced polymer (GFRP) layers. Small-scale columns were prepared and corroded by an accelerated corrosion process. After strengthening, compressive strength tests were carried out on control and weathered specimens. In this research, a marine simulator was designed and constructed similar to the tidal zone of marine environment in south of Iran which was selected as a case study in this research. Mechanical properties of wrapped specimens were studied after placing them inside the simulator for 3000 hours. Marine environment decreased ultimate strength by 4.5% and 26.3% in CFRP and GFRP-wrapped columns, respectively. In some corroded-columns, strengthening was carried out after replacing damaged cover by self-compacted mortar. In this method, by confining with one layer of CFRP and GFRP, 4.2% and 22.4% reduction in ultimate strength was observed, respectively, after exposure. Furthermore, the elastic-brittle behavior has been verified in this retrofit method. Also results of tension tests revealed, the ultimate tensile strength was degraded by 2% and 28.8% in CFRP and GFRP sheets, respectively, after applying marine exposure.